1. Field of the Invention
The present invention relates to an engine speed control unit for controlling the engine speed of an internal combustion engine so that it can reach a target value.
2. Background Art
It is important to control the engine speed of an internal combustion engine so that it can reach a target value.
For example, in the case of an automobile, in order to purify exhaust gas to be cleaner or in order to improve drivability, it is necessary to control the engine speed of an internal combustion engine so that it can reach the target value in various conditions.
For example, as the engine speed of an internal combustion engine after the engine has started greatly affects the exhaust gas, that is, as the engine speed of an internal combustion engine in the period from the completion of the initial combustion at starting to the steady state of idling of the engine greatly affects the exhaust gas, it is necessary to control the engine speed after the start of the engine so that the engine speed can reach the target value.
In this connection, one of the reasons why the engine speed fluctuates after the start of an engine is that a failure in burning occurs in a cylinder. Accordingly, in order to prevent the engine speed from fluctuating after the start of an engine, it is necessary to detect the burning state in a cylinder after the engine has started and control the engine speed so that burning can be conducted properly. In order to control the engine speed of an internal combustion engine so that burning can be conducted properly, Japanese Unexamined Patent Publication No. 62-3139 discloses a device by which the degree of throttle opening is controlled to a target value corresponding to the temperature of an internal combustion engine at the start.
However, when a quantity of suction air is changed in the case of a failure in burning, the burning state is further deteriorated. The reason is described as follows. The failure in burning at the start of an engine is caused by a lean air/fuel ratio because fuel is not sufficiently atomized at the start of an engine but adheres onto a wall face of a suction port so that a sufficient quantity of fuel can not be introduced into a combustion chamber. When the degree of throttle opening is controlled so that it can be increased, negative pressure in a suction tube is reduced, and fuel atomization is further deteriorated and the air/fuel ratio becomes much leaner.
The engine speed of an internal combustion engine in the idling steady state greatly affects the exhaust gas. Therefore, it is also necessary to control the engine speed in the idling steady state so that it can reach the target value. In order to accomplish the above object, Japanese Unexamined Patent Publication No. 5-222997 discloses a suitable device. In this device, in the case of a failure of the suction air feedback control system, it is changed over to the ignition timing feedback control system, and when the engine temperature is low, ignition timing feedback control is subjected to restriction.
In the device disclosed in the above unexamined patent publication, in the case of a failure of the suction air feedback control system, it is changed over to the ignition timing feedback control system, however, even if a failure in burning is caused by feedback control conducted by the suction air feedback control system, it is impossible to detect the failure in burning.
Even if a load given to the engine is changed, it is necessary to keep the engine speed at the target value. In order to accomplish the object, Japanese Unexamined Patent Publication No. 59-3135 discloses a device by which feedback control is conducted so that the idling engine speed can be the target value by increasing the rate of control. However, according to the device of the above unexamined patent publication, it is disclosed that the rate of control is increased with respect to the fluctuation of a load given to the engine, however, the device is provided with only a feedback control means conducted by a quantity of suction air. Therefore, it is impossible to conduct feedback control with a parameter other than the quantity of suction air.
Japanese Unexamined Patent Publication No. 62-210240 discloses a device. In this device, in the case where the temperature of engine coolant is low, suction air feedback control is stopped and open control is conducted while the suction air is fixed at a value corresponding to the temperature of engine coolant. This device is characterized in that learning is conducted in the case of obtaining a value corresponding to the temperature of engine coolant. According to the device of the above unexamined patent publication, a quantity of suction air in the case where suction air feedback control is stopped and open control is conducted can be found by learning, and this open control can comply with a change with time or a difference between each products.
However, even in the process of suction air feedback control, of course, control is affected by the change with time or the difference between each products. Therefore, for example, in the case where the engine speed is subjected to feedback control by adding a correction value to a reference value of suction air quantity, a difference between the required value and the reference value is increased by the change with time or the difference between individual bodies. Accordingly, the correction value is increased. As a result, it takes a long period of time for the engine speed to reach the target value.
However, it is impossible for the device of the above unexamined patent publication to solve the above problems although learning is conducted by the device.
In view of the above problems, it is an object of the present invention to provide an engine speed control unit capable of controlling the engine speed so that it can reach the target value.
It is another object of the present invention to provide an engine speed control unit capable of controlling the engine speed at the start of the engine so that it can reach the target value. It is still another object of the present invention to provide an engine speed control unit capable of controlling the engine speed in the idling steady state so that it can reach the target value. It is still another object of the present invention to provide an engine speed control unit capable of controlling the engine speed so that it can reach the target value even if a load give to the engine fluctuates. It is still another object of the present invention to provide an engine speed control unit capable of controlling the engine speed in the idling steady state so that it can reach the target value. It is still another object of the present invention to provide an engine speed control unit capable of removing influences of a change with time and a difference in individual bodies upon feedback control of the engine speed.
The present invention provides an engine speed control unit of an internal combustion engine for controlling an engine speed so that it can reach a target, comprising: a first engine speed control means for controlling the engine speed by changing a quantity of suction air; a second engine speed control means for controlling the engine speed by changing a control value of a control parameter except for the quantity of suction air; and a burning state judgment means (also referred to as a means for judging a burning state), wherein the engine speed is controlled by the first engine speed control means in the case of a good burning state, and control by the first engine speed control means is stopped and the engine speed is controlled by the second engine speed control means in the case of a bad burning state.
In the engine speed control unit composed as described above, in the case of a good burning state, a quantity of suction air is changed by the first engine speed control means so as to control the engine speed. In the case of a bad burning state, the first engine speed control means stops controlling, and another control parameter, other than the quantity of suction air, is changed by the second engine speed control means without changing the quantity of suction air, so that the engine speed can be controlled. Therefore, the quantity of suction air is not changed and the burning state is not further deteriorated.
According to one aspect of the present invention, after the engine has been set in motion, that is, in a period from the completion of initial combustion at starting to an idling steady state, the engine speed is controlled so that it can reach a target value. Therefore, the first engine speed control means is made to be a first after-start engine speed control means for controlling the after-start engine speed, which is an engine speed from the completion of initial combustion at Starting to the idling steady state, so that the after-start engine speed can show a target change characteristic in the case where the burning state is judged to be good, the second engine speed control means is made to be a second after-start engine speed control means for controlling the after-start engine speed, which is an engine speed from the completion of explosion at the engine start to the idling steady state, so that the after-start engine speed can show a target change characteristic in the case where the burning state is judged to be bad, and the after-start engine speed from the completion of explosion at the engine start to the idling steady state is controlled.
In this case, for example, the second after-start engine speed control means changes at least one of the control values of ignition timing, quantity of fuel injection and fuel injection timing.
Further, an engine speed control unit of an internal combustion engine comprises a bad burning cylinder judgment means for judging a bad burning cylinder, wherein, when it is judged to be a bad burning state, the bad burning cylinder is distinguished from other cylinders and controlled by the second after-start engine speed control means so that the engine speed can show a target change characteristic.
According to another aspect of the present invention, after the engine has been set in motion, that is, in a period from the completion of explosion to an idling steady state, the engine speed is controlled so that it can reach a target value. Therefore, the first engine speed control means is made to be a first idling engine speed control means for controlling the engine speed in the idling steady state so that it can reach the target value by feedback control in the case where the burning state is judged to be good, the second engine speed control means is made to be a second idling engine speed control means for controlling the engine speed in the idling steady state so that it can reach the target value in the case where the burning state is judged to be bad, and the engine speed in the idling steady state is controlled so that it can reach the target value.
In this case, for example, when it is judged to be a bad burning state and the idling engine speed control by the first idling engine speed control means is stopped and the idling engine speed control by the second idling engine speed control means is executed, the feedback control by the first idling engine speed control means is executed again after that, the burning state is rejudged by the burning state judgment means in this state and, when it is again judged to be a bad burning state in the rejudgment of the burning state, the idling engine speed control is executed by the second engine speed control means.
The idling engine speed control executed by the second engine speed control means after the rejudgment of the burning state is conducted by the same parameter as that of the idling engine speed control executed by the second engine speed control means before the rejudgment of the burning state while the control value is being changed.
The idling engine speed control executed by the second engine speed control means after the rejudgment of the burning state is conducted by a different parameter from that of the idling engine speed control executed by the second engine speed control means before the rejudgment of the burning state.
The idling engine speed control conducted by the second engine speed control means before the rejudgment of the burning state and the idling engine speed control conducted by the second engine speed control means after the rejudgment of the burning state are executed being selected so that the idling engine speed control, the influence given to exhaust gas emission of which is smaller, is executed first.
Further, the engine speed control unit of an internal combustion engine comprises a bad burning cylinder discrimination means for discriminating a cylinder in a bad burning state, wherein when it is judged to be a bad burning state, the bad burning cylinder is discriminated from other cylinders and controlled by the second engine speed control means.
The idling engine speed control conducted by the second engine speed control means is also feedback control.
The idling engine speed control conducted by the second engine speed control means is a quantitative change control by which the control parameter is changed by a predetermined value so that the control parameter cannot exceed a guard value.
The internal combustion engine is provided with an air/fuel ratio feedback control means for controlling an air/fuel ratio by feedback control, and the idling engine speed is controlled by the first idling engine speed control means when the air/fuel ratio feedback control means is operated.
The idling engine speed is controlled by the first idling engine speed control means when the engine temperature is higher than a predetermined value.
The idling engine speed is controlled by the first idling engine speed control means when the lapse of time after the start of the engine is more than a predetermined value.
The burning state judgment means judges a burning state from a change in the engine speed with respect to a change in the quantity of suction air of feedback control conducted by the first engine speed control means.
According to another aspect of the present invention, in order to control the engine speed so that it can reach the target even when a load given to the engine is fluctuating, the first engine speed control means conducts feedback-control so that the engine speed in the idling steady state can be a target value when it is judged to be a good burning state, and the second engine speed control means continues feedback-control so that the engine speed can be an after-load-change engine speed target value, which has been previously set, when a load is changed in the process of executing engine speed control by the second engine speed control means.
In this case, for example, the after-load-change engine speed target value is the same as the before-load-change engine speed target value.
Alternatively, the after-load-change engine speed target value is different from the before-load-change engine speed target value.
Alternatively, an engine speed control unit of an internal combustion engine further comprises a load change detection means, wherein the after-load-change engine speed target value is determined by a change in the load.
Alternatively, the after-load-change control reference value corresponding to the after-load change engine speed target value is set, and the second engine speed control means conducts feedback control on the basis of the after-load-change control reference value.
Alternatively, an engine speed control unit of an internal combustion engine further comprises a load change detection means, wherein the after-load-change control reference value is determined by a change in the load.
Alternatively, the second engine speed control means conducts feedback control on the idling engine speed by one of the control parameters of the ignition timing and the quantity of fuel injection before a change in the load, and the second engine speed control means conducts feedback control on the engine speed by the same control parameter as that of before a change in the load even after a change in the load.
According to another aspect of the present invention, in order to remove the influence of a change with time and a difference in individual products on the feedback control of the engine speed, an engine speed control unit of an internal combustion engine according to claim 1, further comprises: a parameter reference value learning means for renewing and storing a parameter reference value according to a state of operation; a parameter correction value calculating means for calculating a parameter correction value necessary for making the engine speed close to a target value; and a parameter control means for controlling a parameter so as to provide a parameter execution value in which the parameter correction value is added to the parameter reference value, wherein the parameter reference value learning means renews a parameter reference value so that the parameter correction value can be reduced in the case where the parameter correction value exceeds a predetermined range, and the engine speed of the internal combustion engine is controlled so that it can reach a target value by feedback control of the control parameter selected according to the state of burning.
In this case, for example, the parameter reference value learning means stores a parameter reference value according to at least one of the engine temperature, the shift position of a transmission connected with the engine and the state of operation of the accessories.
Alternatively, a quantity of suction air is selected as a control parameter in the case of a good burning state.
Alternatively, ignition timing or a quantity of fuel injection is selected as a control parameter in the case of a bad burning state.